Method and/or apparatus for cross-color and cross-luminance suppression using shimmer detection

ABSTRACT

An apparatus comprising one or more delay circuits, a shimmer detector circuit, an averaging circuit, and a multiplexer. The delay circuits may be configured to have a delay of one or more frame periods based on the format of the input video signal. The shimmer detector circuit may be configured to (i) determine which pixel locations in the input video signal exhibit the YC-interference noise oscillation pattern based on the input signal and the output of the delay circuits and (ii) generate a control signal in response to the output of the delays circuits and the input signal. The averaging circuit may be configured to calculate an average of the input signal and the output of the first delay circuit. The multiplexer may be configured to present (i) the input signal when the control signal is in a first state and (ii) the average signal when the control signal is in a second state.

This application claims the benefit of U.S. Provisional Application No.60/740,860, filed Nov. 30, 2005 and is hereby incorporated by referencein its entirety.

FIELD OF THE INVENTION

The present invention relates to video processing generally and, moreparticularly, to a method and/or apparatus for cross-color andcross-luminance suppression using shimmer detection.

BACKGROUND OF THE INVENTION

In composite video signals, the luminance and chrominance signals aretransmitted in the same bandwidth. The chrominance signal is modulatedonto a sub-carrier signal and then added to a luminance signal to createa baseband signal. The baseband signal is then modulated onto a carrierfor transmission. At the decoder, the baseband signal must be processedto separate the chrominance and luminance signals. Some mixing of thetwo signals is unavoidable, resulting in YC-interference noise, alsocalled cross-color and cross-luminance. Cross-color is the result ofdecoding part of the luminance signal as color data. The changes in thesub-carrier phase cause the YC-interference noise to affect the decodeddigital signal in a predictable way. For still pixels (pixels whoseideal, noise-free component values are not changing between frames), thevalue of the YC-interference noise in the decoded cross-luminance is theresult of decoding part of the color signal as luminance data.

For both National Television System Committee (NTSC) and phasealternating line (PAL) transmission standards, the phase of the colorsub-carrier changes with each frame in a specified pattern. For NTSC,the phase of the color sub-carrier inverts every frame. As a result, inunchanging “still” pixel locations, YC-interference noise causes thecomponents of the pixel location to oscillate about an ideal value atthe frame rate. Such an oscillating effect which is often referred to asshimmering is illustrated by the following equations:y _(F) _(—) _(in[T]) =y _(id) +y _(c) y _(F) _(—) _(in[T−2]) =y _(id) −y_(c) y _(F) _(—) _(in[T−4]) =y _(id) +y _(c)cr _(F) _(—) _(in[T]) =cr _(id) +cr _(y) cr _(F) _(—) _(in[T−2]) =cr_(id) −cr _(y) cr _(F) _(—) _(in[T−4]) =cr _(id) +cr _(y)cb _(F) _(—) _(in[T]) =cb _(id) +cb _(y) cb _(F) _(—) _(in[T−2]) =cb_(id) −cb _(y) cb _(F) _(—) _(in[T−4]) =cb _(id) +cb _(y)where

-   -   Y_(id), cr_(id), cb_(id)—Ideal value of components of the pixel        location    -   Y_(c), cr_(y), cb_(y)—Absolute value of YC-interference noise    -   F_in[t]—The Sequence of input video fields    -   T—The index of the most recent input field

The ideal value of still pixel locations can be recovered by averagingthe pixel values in adjacent fields. FIGS. 1 and 2 illustrate thepattern of the color sub-carrier phase change in NTSC video and theresulting pattern in the YC-interference noise at still pixel locations.

For PAL, the phase of the color sub-carrier shifts by 90° every frame sothat the sub-carrier inverts every 2 frames. YC-interference noise atunchanging pixel locations causes the actual value of the pixel tooscillate around the ideal value at half the frame rate, as shown by thefollowing equations:y _(F) _(—) _(in[T]) =y _(id) +y _(c) y _(F) _(—) _(in[T−4]) =y _(id) −y_(c) y _(F) _(—) _(in[T−8]) =y _(id) +y _(c)cr_(F) _(—) _(in[T]) =cr _(id) +cr _(y) cr _(F) _(—) _(in[T−4]) =cr_(id) −cr _(y) cr _(F) _(—) _(in[T−8]) =cr _(id) +cr _(y)cb _(F) _(—) _(in[T]) =cb _(id) +cb _(y) cb _(F) _(—) _(in[T−4]) =cb_(id) −cb _(y) cb _(F) _(—) _(in[T−8]) =cb _(id) +cb _(y)

The ideal value of still pixel locations can be recovered by averagingthe pixel values in fields T and T−4. FIGS. 3 and 4 illustrate thepattern of the color sub-carrier phase changes in PAL video and theresulting pattern in the YC-interference noise at still pixel locations.

The effect of the changing phase of the color sub-carrier on theYC-interference noise makes it possible to use temporal filtering toeliminate the cross-luminance and cross-color in the separated luminanceand chrominance signals. Because non-adaptive temporal filtering causesvisual artifacts in moving areas of the video, some method of adaptingthe filter to prevent those artifacts is needed. One conventionalapproach uses a motion detector to switch the filter off in areas of thevideo that have motion. Such a conventional approach is shown in FIG. 5.The problem with such an approach is that the YC-interference noise thatthe filter is trying to eliminate can cause motion detectors toincorrectly label still areas as motion areas.

It would be desirable to implement a detector that identifies andfilters particular pixels whose components exhibit the oscillationpattern caused by YC-interference noise.

SUMMARY OF THE INVENTION

The present invention concerns an apparatus comprising one or more delaycircuits, a shimmer detector circuit, an averaging circuit, and amultiplexer. The one or more delay circuits may be configured togenerate a delay of one or more frame periods in response to the formatof an input signal. The shimmer detector circuit may be configured to(i) determine which pixel locations in the input signal exhibit anoscillation pattern in their component values and (ii) generate acontrol signal in response to the outputs of the delay circuits and theinput signal. The averaging circuit may be configured to calculate anaverage signal in response to the input signal and the output of thefirst delay circuit. The multiplexer may be configured to present (i)the input signal and (ii) the average signal in response to the controlsignal from the shimmer detector circuit.

The objects, features, and advantages of the present invention includeproviding a method and/or apparatus of removing YC-interference noisefrom post-separation video signals that (i) does not reduce the verticalor horizontal resolution of the video, (ii) filters only those pixellocations affected by noise without causing artifacts in the presence ofmotion and/or (iii) is effective in the presence of strongYC-interference noise.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other objects, features and advantages of the presentinvention will be apparent from the following detailed description andthe appended claims and drawings in which:

FIG. 1 is a diagram illustrating the pattern of change in the colorsub-carrier phase for NTSC video;

FIG. 2 is a diagram illustrating the oscillation pattern in thecomponent values of still pixel locations caused by YC-interferencenoise as a result of the color-subcarrier phase pattern in NTSC video.

FIG. 3 is a diagram illustrating the pattern of change in the colorsub-carrier phase for PAL video;

FIG. 4 is a diagram illustrating the oscillation pattern in thecomponent values at still pixel locations caused by, YC-interferencenoise as a result of the color-subcarrier phase pattern in PAL video;

FIG. 5 is a diagram illustrating a conventional temporal comb filterusing a motion detector;

FIG. 6 is a diagram illustrating a preferred embodiment of the presentinvention;

FIG. 7 is a diagram illustrating a component value of a shimmering pixellocation (NTSC);

FIG. 8 is a diagram illustrating a component value of a shimmering pixellocation (PAL); and

FIG. 9 is a diagram illustrating changes to a shimmer value of a pixellocation over time under different conditions.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMRNTS

Referring to FIG. 6, a block diagram of a circuit 100 is shown inaccordance with a preferred embodiment of the present invention. Thecircuit 100 generally comprises a block (or circuit) 102, a block (orcircuit) 104, a block (or circuit) 106 and a block (or circuit) 108. Thecircuit 102 may be implemented as a delay circuit. In one example, thecircuit 102 may be implemented as a 2/4 field delay circuit. Similarly,the circuit 104 may be implemented as a delay circuit. In one example,the circuit 104 may be implemented as a 2/4 field delay circuit. Thecircuit 106 may be implemented as a detector circuit. In one example,the circuit 106 may be implemented as a shimmer detector circuit. Thecircuit 108 may be implemented as a multiplexer circuit. The circuit 102may have an input 110 that receives an input signal. The circuit 102 mayhave an output 112 that presents a signal to an input 114 of the circuit104. The circuit 104 may have an output 116. The output 112 may also bepresented to an input 118 of an adder circuit 120. The adder circuit 120may also have an input 121 that may receive the input signal. The inputsignal may also be presented to an input 122 of the shimmer detector106. The shimmer detector 106 may also have an input 124 that mayreceive the input signal and an input 126 that may receive a signal fromthe circuit 102. The adder 120 may present an output to a circuit 130.The circuit 130 may be a divide-by-two circuit. The circuit 130 maypresent a signal (e.g., AVG) to the input 132 of the multiplexer. Themultiplexer 108 may also have an input 134 that receives the inputsignal. The shimmer detector 106 may present a signal (e.g., CTR) to acontrol input 136 of the multiplexer 108. An averaging circuit generallycomprises the adder circuit 118 and the divide-by-two circuit 130. Thedelay circuit 104 and the delay circuit 106 may delay one or more frameperiods based on the format (e.g., NTSC or PAL) of the input signal. Thedelay circuit 102 may present a first delay of one or more frame periodsto the adder circuit 120 and the shimmer detector circuit 120. The delaycircuit 104 may present a second delay of one or more frame periods tothe shimmer detector 106. Each component (y, cr and cb) is averagedseparately. The averaging circuit may provide a filtered signal (e.g.,AVG) that is free of YC-interference noise in still pixel locations. Theideal values of a still pixel location's components may be recovered inthe presence of YC-interference noise by averaging the components'current values with the components'values from 2 or 4 fields previous.

The circuit 100 may use the shimmer detector circuit 106 to identify thepixel locations in the input video frame on the input video signal whosecomponents which exhibit the oscillation pattern caused byYC-interference noise at still pixel locations. The circuit 100 allowsfiltering of only the affected pixels. Since the oscillation patternonly occurs in pixels having ideal values that are unchanging (e.g.,pixels in still areas), the circuit 100 avoids creating motionartifacts.

The shimmer detector 106 generally looks for pixel component values thatoscillate with a constant amplitude around a fixed value at half (e.g.,for NTSC) or one-quarter (e.g., for PAL) the frame rate as a result ofYC-interference. To detect such oscillation, it may be necessary toexamine the component values of a particular pixel over a period oftime. Because random noise and motion in the video can cause thecomponent values of the pixel to mimic the YC-interference oscillationpattern over short intervals, this period of time is greater than thetime which may be stored in the delay circuit 102 and the delay circuit104. To overcome this problem, the shimmer detector 106 may implement atwo-tier “shimmer test”. The first tier is a “short-term” test thatexamines each locations' component values over a short period of time tomake a tentative identification of those still locations that are“shimmering” (e.g., oscillating as a result of YC-interference noise).The second tier uses a “shimmer value” for each pixel location to trackthe results of the short-term test over a longer period of time in orderto make a final determination of the shimmer status of each location.The delay circuit 102 and the delay circuit 104 provide a short-termhistory of the component values for each pixel location that may be usedby the shimmer detector 106 for the short-term test. The shimmerdetector 106 may provide the results of the two-tier shimmer test on thesignal CTR. The signal CTR may change at the pixel frequency in responseto the results of the shimmer test for each pixel location in everyframe. If the shimmer detector 106 determines that a pixel location isshimmering for the current input frame, the signal CTR will select thesignal AVG as the output of the multiplexer 108. If the shimmer detector106 determines that a pixel location is not shimmering, the signal CTRwill select the input signal as the output of the multiplexer 108. Thedelays of the paths from the input 100 to the inputs 132, 134, and 136on the multiplexer 108 should be equal in order to synchronize the CTRsignal with the correct signals on 132 and 134.

FIGS. 7 and 8 illustrate the value over time of a component of a stilland shimmering pixel location in an NTSC signal and a PAL signal,respectively. A “target pixel” refers to the component values of a pixellocation in the current input field (e.g., the target field). An“out-of-phase pixel” refers to the components values of a pixel locationin the most recent input field that is the same polarity (even or odd)as the target field and has a color sub-carrier phase that is 180°out-of-phase with the sub-carrier phase of the target field (e.g., theout-of-phase field). An “in-phase pixel” refers to the components valuesof a pixel location in the most recent input field that is the samepolarity as the target field and has a color sub-carrier phase that isin-phase with the sub-carrier phase of the target field (e.g., thein-phase field). In the ideal (e.g., no random noise) case, if the pixellocation is still and shimmering, then the component values of the pixelwill be shown in TABLE 1 with at least one of y_(c), cr_(y), or cb_(y)being greater than zero:

TABLE 1 Target Out-of-Phase In-Phase y_(id) + y_(c) y_(id) − y_(c)y_(id) + y_(c) cr_(id) + cr_(y) cr_(id) − cr_(y) cr_(id) + cr_(y)cb_(id) + cb_(y) cb_(id) − cb_(y) cb_(id) + cb_(y)The absolute differences between the component values of the targetpixel and the component values of the in-phase pixels (e.g., thein-phase differences) will be zero. In a non-ideal case, noise and otherimperfections in the system may invariably cause the in-phasedifferences to be greater than zero.

For the short-term shimmer test, the shimmer detector 106 may comparethe target pixel, the out-of-phase pixel, and the in-phase pixel for thepixel location. A pixel location may be considered to exhibit a “shimmerpattern” for the target field if (i) the target pixel and the in-phasepixel match (e.g., the component values are close) and (ii) thedifference between the target pixel and the out-of-phase pixel isgreater than the difference between the target pixel and the in-phasepixel. More precisely, the pixel location [n,k] exhibits a shimmerpattern for the target field F_in[T] if(i)(ipDiffY<=YMatchTh)and(ipDiffCr<=CrMatchTh)  EQ1

and(ipDiffCb<=CbMatchTh); and(ii)(opDiffY>ipDiffY)or(opDiffCr>ipDiffCr) or(opDiffCb>ipDiffCb)  EQ 2where [n,k] represent the horizontal and vertical indices of the pixellocation in a video frame. Even fields includes locations with even ks.Odd fields include locations with odd ks. As a result, only half of thelocations in the frame may be tested during each input field period. Thevariables ipDiffY, ipDiffCr, and ipDiffCb may be defined as the in-phasedifferences for the components y, cr and cb of the pixel locationrespectively. The variables opDiffY, opDiffCr, and opDiffCb may bedefined as the out-of-phase differences for the components y, cr and cbof the pixel location respectively. In equation form, the out-of-phasedifferences may be-defined as follows:opDiffY=|y _(F) _(—) _(in[T]) [n,k]−y _(F) _(—) _(in[Top]) [n,k]|opDiffCr=|cr _(F) _(—) _(in[T]) [n,k]−cr _(F) _(—) _(in[Top]) [n,k]|opDiffCb=|cb _(F) _(—) _(in[T]) [n,k]−cb _(F) _(—) _(in[Top]) [n,k]|where (i) y_(F) _(—) _(in[T])[n,k], cr_(F) _(—) _(in[T])[n,k], andcb_(F) _(—) _(in[T])[n,k] may be defined as the components, y, cr and cbrespectively, of the target pixel (F_n[T][n,k]), and (ii) y_(F) _(—)_(in[Top])[n,k], cr_(F) _(—) _(in[Top])[n,k] and cb_(F) _(—)_(in[Top])[n,k] may be defined as the components, y, cr and cb of theout-of-phase pixel (F_in [Top] [n,k]).

Likewise, the in-phase differences may be defined as follows:ipDiffY=|y _(F) _(—) _(in[T]) [n,k]−y _(F) _(—) _(in[Tip]) [n,k]|ipDiffCr=|cr _(F) _(—) _(in[T]) [n,k]−cr _(F) _(—) _(in[Tip]) [n,k]|ipDiffCb=|cb _(F) _(—) _(in[T]) [n,k]−cb _(F) _(—) _(in[Tip]) [n,k]|where y_(F) _(—) _(in[Tip])[n,k], cr_(F) _(—) _(in[Tip])[n,k], andcb_(F) _(—) _(in[Tip])[n,k]may be defined as the components, y, cr andcb respectively, of the in-phase pixel (F_in[Tip] [n,k]).

The variables YMatchTh, CrMatchTh, and CbMatchTh are thresholds thatdetermine the maximum in-phase difference, for y, cb and crrespectively, that is allowed before the target and in-phase pixel areno longer considered to “match”.

The rejection by the short term shimmer test of oscillations caused bynoise may be improved by modifying the second condition (or EQ2) asfollows:(ii) [(opDiffY>ipDiffY) and (opDiffY>YNoiseTh)] or[(opDiffCr>ipDiffCr) and (opDiffCr>CrNoiseTh)] or[(opDiffCb>ipDiffCb) and (opDiffCb>CbNoiseTh)]where YNoiseTh, CrNoiseTh, and CbNoiseTh may be defined as noisethresholds that may determine the minimum out-of-phase difference, fory, cr and cb respectively, that may be considered to have been caused byYC-interference oscillation. If the out-of-phase difference is less thanthe threshold then the out-of-phase difference may be considered to havebeen caused by random noise.

For the second tier of the shimmer test, shimmer detector 106 may assigna shimmer value to each pixel location in the input video frame in orderto track the results of the short term test over time. The shimmer valuefor each pixel location may be increased or decreased each input videoframe based on the result of the short-term shimmer test for thatparticular frame. If the short-term shimmer test detects a shimmerpattern, then the shimmer value is increased. Otherwise, the shimmervalue is decreased. When the shimmer value exceeds a shimmer threshold(e.g., ShimTh), the location is considered to be shimmering for thatparticular frame.

The method of accumulating and decaying the shimmer value needs toprovide for (i) a reasonably fast detection time, (ii) insensitivity torandom noise, and (iii) robustness against false detections caused bymotion. A geometric accumulation and decay has been found to providegood results.

The shimmer value for pixel location [n,k] is adjusted for the targetfield T as follows:

if the short-term test detects a shimmer pattern for the location,(i) shimVal[n,k][T]=a+d*shimVal[n,k][T−2];otherwise, (ii) shimVal[n,k][T]=d*shimVal[n,k][T−2]where (i) shimVal[n,k] may be defined as the shimmer value for pixellocation [n,k], (ii) shimVal[n,k][T] may be defined as the value of theshimmer value after adjustment for the result of the short-term shimmertest for field T, (iii) shimVal[n,k][T−2] may be defined as the value ofthe shimmer value after adjustment for field T−2 (the value after theprevious frame), (iv) ‘d’ may be defined as the decay coefficient andmay have a value 0<d<1, and (v) ‘a’ may be defined as the accumulationconstant and may have a value a=(Maximum value of shimVal[n,k])*(1−d).FIG. 9 illustrates the changes to a shimmer value over time using theaccumulation and decay method outlined above. The shimmer detector 106may consider a pixel location [n,k] to be shimmering for the targetfield T if shimVal[n,k][T]>=ShimTh.

Referring to FIG. 9, the shimmer detector circuit 106 may change thesignal CTR each pixel period based on the result of the shimmer test foreach pixel location. For example, when the component values for pixellocation [n,k] for the current input field T are on input 134 of themultiplexer 108 and the corresponding filtered component values (e.g.,signal AVG) are on input 132, shimmer detector 106 may set the signalCTR to select an output for 108 based on the shimmer-test result of thelocation [n,k] for the field T. The shimmer detector 106 selects thesignal AVG on input 132 with the signal CTR if the location [n,k] isshimmering for the field T. Otherwise, the shimmer detector 106 selectsthe unfiltered input signal on input 134.

The present invention generally implements a shimmer detector toidentify pixels locations whose components exhibits an oscillationpattern caused by YC-interference noise. The present invention filtersonly the affected pixels. Since the oscillation pattern only occurs forpixel locations whose ideal values are not changing (e.g., pixels instill areas), the present invention generally avoids motion artifacts.

The present invention may (i) implement the shimmer detector with amotion detector (ii) use the shimmer-test results of adjacent pixellocations to modify the shimmer value of a pixel location and/or (iii)extend the time window used for the short-term shimmer test.

While the invention has been particularly shown and described withreference to the preferred embodiments thereof, it will be understood bythose skilled in the art that various changes in form and details may bemade without departing from the spirit and scope of the invention.

1. An apparatus comprising: one or more delay circuits configured togenerate a delay of one or more frame periods in response to a format ofan input signal; a shimmer detector circuit configured to (i) determinewhich pixel locations in said input signal exhibit an oscillationpattern based on one or more component values of said pixel locationsand (ii) generate a control signal in response to one or more outputs ofsaid delay circuits and said input signal; an averaging circuitconfigured to calculate an average signal in response to said inputsignal and an output of the first delay circuit; and a multiplexerconfigured to present (i) said average signal when said control signalis in a first state and (ii) said input signal when said control signalis in a second state.
 2. The apparatus according to claim 1, whereinsaid shimmer detector circuit is configured to determine which of saidpixel locations in said input signal exhibit said oscillation patternbased on said component values of said pixel locations in predeterminedframe periods effected by YC-interference noise.
 3. The apparatusaccording to claim 1, wherein said component values oscillate at a fixedvalue at (i) half the frame rate for National Transmission SystemCommittee transmission standards and (ii) one-quarter the frame rate forphase alternating line (PAL) transmission standards the frame rate dueto YC-interference noise.
 4. The apparatus according to claim 1, whereinsaid one or more delay circuits provides a short-term history of saidcomponent values for each pixel location.
 5. The apparatus according toclaim 4, wherein said shimmer detector circuit is configured to (i)examine said short term history of said pixel location and (ii)tentatively identify said pixel locations that are shimmering.
 6. Theapparatus according to claim 5, wherein said shimmer detector circuit isconfigured to designate said pixel location as shimmering in response todetermining if said pixel location has been tentatively shimmering for apredetermined amount of time.
 7. The apparatus according to claim 6,wherein said multiplexer is configured to present said input signal ifsaid pixel location is not determined to be shimmering.
 8. The apparatusaccording to claim 6, wherein said multiplexer is configured to presentsaid average signal if said pixel location is determined to beshimmering.
 9. The apparatus according to claim 8, wherein said shimmerdetector circuit makes a tentative identification of said pixellocations by (i) comparing a component value of a target pixel to acomponent value of an in-phase pixel and (ii) determining whether thedifference between the component levels of said target pixel and anout-of-phase pixel is greater than the difference of the componentlevels of said target pixel and said in-phase pixel.
 10. The apparatusaccording to claim 9, wherein said shimmer detector circuit isconfigured to assign a shimmer value to each pixel location on saidinput signal to track a shimmer history.
 11. The apparatus according toclaim 10, wherein said shimmer detector circuit increases or decreasessaid shimmer value based on whether said pixel location meets a shimmerpattern criteria.
 12. The apparatus according to claim 11, wherein saidshimmer detector circuit is configured to (i) increase said shimmervalue if said shimmer value of said pixel location is greater than anaveraging threshold and (ii) decrease said shimmer value of said pixellocation is less than said averaging threshold.
 13. A method forpost-separation comb filtering using shimmer detection, comprising thesteps of: (A) generating a delay of one or more frame periods inresponse to a format of an input signal; (B) determining which pixellocations is said input signal exhibit an oscillation pattern based oncomponent values of said pixel locations; (C) generating a controlsignal in response to said delays from step (A) and said input signal;(D) calculating an average signal in response to said input signal and afirst of said delays from step (A); and (E) presenting (i) said inputsignal when said control signal is in a first state and (ii) saidaverage signal when said control signal is in a second state.
 14. Themethod according to claim 13, wherein step (C) further comprises thestep of: determining which of said pixel locations in said input signalexhibit an oscillation pattern based on said component values whichoscillate at half the frame rate for National Television SystemCommittee (NTSC) transmission standards; and determining which of saidpixel locations in said input signal exhibit an oscillation patternbased on said component values which oscillate at one-quarter the framerate for phase alternating line (PAL) transmission standards.
 15. Themethod according to claim 13, wherein step (C) further comprises thestep of: examining a short term history of for each pixel location; andtentatively identifying said pixel locations that is shimmering.
 16. Themethod according to claim 15, further comprising the step of:designating a pixel location as shimmering in response to determiningwhether said pixel location has been tentatively shimmering for apredetermined amount of time.
 17. The method according to claim 16,further comprising the step of: comparing a component value of a targetpixel to a component value of an in-phase pixel; and determining whetherthe difference between said component values of said target pixel and anout-of-phase pixel is greater than the difference of the componentlevels of said target pixel and said in-phase pixel.
 18. The methodaccording to claim 17, further comprising the step of: assigning ashimmer value to said pixel location on said input signal to track ashimmer history.
 19. The method according to claim 18, furthercomprising the step of: increasing said shimmer value if said shimmervalue of said pixel location is greater than an averaging threshold; anddecreasing said shimmer value if said shimmer value of said location ofsaid pixel location is less than said averaging threshold.
 20. Anapparatus comprising: means for generating one or more delays for one ormore frame periods in response to a format of an input signal; means fordetermining which pixel locations in said input signal exhibit anoscillation pattern based on component values of said pixel locations;means for generating a control signal in response to said input signaland said delays; means for calculating an average signal in response tosaid input signal and a first of said delays of one or more frameperiods; and means for presenting (i) said input signals when saidcontrol signal is in a first state and (ii) said average signal whensaid control signal is in a second state.